1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device that can reduce the brightness deviation among pixel cells in a 2-dot inversion system and a method for driving the same.
2. Discussion of the Related Art
Typically, liquid crystal display (LCD) devices display an image by controlling light transmittances of liquid crystal cells. In particular, in an active matrix LCD device, there is an advantage in displaying video images because switching devices are provided for respective liquid crystal cells. For such switching devices, thin film transistors (TFTs) are mainly used.
LCD devices are driven in an inversion mode. The polarity of data charged in each liquid crystal cell is periodically inverted to achieve a reduction in flickers and latent images. There are various inversion methods. For example, in a line inversion method, polarity inversion of data is carried out between liquid crystal cells arranged adjacent to each other in a vertical line direction. In a column inversion method, polarity inversion of data is carried out between liquid crystal cells arranged adjacent to each other in a horizontal line direction. In a dot inversion method, polarity inversion of data is carried out between liquid crystal cells arranged adjacent to each other in both the vertical line direction and the horizontal line direction.
In the dot inversion method, the polarities of data signals respectively supplied to the vertically-adjacent pixel cells are opposite to each other, and the polarities of data signals respectively supplied to the horizontally-adjacent pixel cells are also opposite to each other. In this method, the polarity of each data signal is inverted at intervals of one frame period. In the dot inversion method, generation of flickers is minimized in both the vertical and horizontal directions. Accordingly, this method is applied to most LCD devices commercially available as monitors or televisions. However, the dot inversion method has a drawback. The power consumption is high because the polarity of each data signal should be inverted at intervals of one horizontal period. This problem can be solved by performing driving of a liquid crystal panel in a 2-dot inversion mode.
FIG. 1 is a schematic view showing the 2-dot inversion mode. In the 2-dot inversion method, as shown in FIG. 1, data signals respectively supplied to the pixel cells arranged in a horizontal direction have opposite polarities at intervals of one pixel cell, respectively. On the other hand, data signals respectively supplied to the pixel cells arranged in a vertical direction have opposite polarities at intervals of two pixel cells, respectively. In this method, the polarity of each data signal is inverted at intervals of one frame. For example, the polarity of each data signal is inverted between successive frames Fn and Fn+1, as shown in FIG. 1.
However, the above-mentioned 2-dot inversion method has the following problems. FIG. 2 is a waveform diagram showing problems incurred in the 2-dot inversion method. In order to drive an LCD device in a 2-dot inversion mode, a data signal that exhibits a polarity variation, as shown in FIG. 2, is supplied to a data line. A positive data signal Vdata is supplied to the data line in first and second periods T1 and T2, whereas a negative data signal Vdata is supplied to the data line in third and fourth periods T3 and T4. Also, a positive data signal Vdata is supplied to the data line in fifth and sixth periods T5 and T6.
In this case, the charging of the data line for a duration from the first period T1 to the second period T2 is carried out rapidly because the data signal Vdata supplied to the data line in the first period T1 and the data signal Vdata supplied to the data line in the second period T2 both have a positive polarity. However, the charging of the data line for a duration from the second period T2 to the third period T3 is carried out slowly because the polarity of the data signal Vdata transits from a positive polarity to a negative polarity in the third period T3.
Although there is no problem associated with charging speed when the polarity of the data signal Vdata charged in each data line is not changed, when a transition occurs, there is a reduction in the charging speed because the polarity of the data signal Vdata charged in each data line changes. For example, the polarity changes from a positive state to a negative state, or from a negative state to a positive state when a transition occurs. As a result, there can be a deviation of brightness between pixel cells which are connected to the same data line, but receive data signals Vdata of different polarities.